Mg-8Zn-4Al-1Ca合金的时效微观组织(英文)

利用TEM和HRTEM研究Mg-8Zn-4Al-1Ca合金的时效微观组织。结果表明:Mg-8Zn-4Al-1Ca合金较Mg-8Zn-4A1合金时效硬度显著增高。Mg-8Zn-4Al-1Ca合金在160°C时效16 h,有大量的盘状Ca2Mg6Zn3相沉淀弥散析出,此外,合金的微观组织中还存在晶格畸变、蜂窝状的莫尔条纹、刃型位错及位错环;经48 h时效后合金中沉淀相为粗大的盘状沉淀相和细小、弥散的粒状沉淀相;经227 h时时效后后,其组织中存在大量MgZn2相和Ca2Mg6Zn3相。因此,在Mg-8Zn-4Al-1Ca时效160°C的合金中添加Ca元素能有效提高合金的时效硬度及促进MgZn2强化相的生成。     

Microstructure and compression deformation behavior in the quasicrystalreinforced Mg-8Zn-1Y alloy solidified under super-high pressure

The microstructure of Mg-8Zn-1Y alloy solidified under super-high pressure was analyzed through X-ray diffraction(XRD), scanning electron microscopy(SEM) and energy dispersive spectroscopy(EDS). And, compression deformation behavior at room-temperature was studied. The results showed that the microstructure of Mg-8Zn-1Y alloy solidified under ambient pressure and super-high pressure was both mainly composed of ■-Mg and quasicrystal I-Mg3Zn6 Y. Solidification under super-high pressure contributed to refining solidified microstructure and changing morphology of the intergranular second phase. The morphology of intergranular second phase(quasicrystal I-Mg3Zn6Y) was transformed from continuous network(ambient pressure) to long island(high pressure) and finally to granular(super-high pressure) with the increase in pressure. The compressive strength, yield strength and rupture strain of the samples solidified under ambient pressure were significantly improved from 262.6 MPa, 244.4 MPa and 13.3% to 437.3 MPa, 368.9 MPa and 24.7% under the pressure of 6 GPa, respectively. Under ambient pressure, cleavage plane on compressive fracture was large and smooth. When it was solidified under the pressure ranging from 4 to 6 GPa, cleavage plane on compressive fracture was small and coarse. In addition, dimple, tear ridge and lobate patterns existed.     

8YSZ双层热障涂层缺陷演变与微裂纹水浸超声宏观检测

采用PASCAN-64型水浸超声设备并配合扫描电镜对8wt %Y₂O₃-ZrO₂(8YSZ)双层热障涂层热震过程中内部组织结构演变进行了检测。结果表明, 当超声波从垂直陶瓷层方向入射至粘结层反射所获得的回波信号影像主要反映了陶瓷层组织结构演变, 从垂直基底方向入射至粘接层/陶瓷层界面处反射所获得的回波信号影像主要反映了热生长氧化物层组织结构演变, 从垂直陶瓷层方向透射整个试片所获得的回波信号影像综合反映了整个涂层组织结构演变。当陶瓷层中均匀分布着孔隙率<11%、最大横向尺寸<50 μm的孔隙以及热生长氧化物层主要为致密的α-Al₂O₃时, 回波信号的幅值dB<0, 反映在影像中的信号分布均匀, 表明涂层处于良好状态。当陶瓷层中均匀分布着孔隙率>44%、最大横向尺寸>100 μm的孔隙以及热生长氧化物层主要为具有稀疏结构且厚度>5.2 μm的Cr、Co氧化物时, 回波信号的幅值dB>0的区域连接成片, 则预示着涂层即将失效或已失效。可见, 水浸超声技术能够较准确地反映热障涂层内部组织结构演变, 是一种较好的热障涂层内部缺陷的无损检测方法。     

GPa级超高压下Mg-6Zn-1Y合金晶体形态及凝固组织分析

利用扫描电镜（SEM）并配合能谱（EDS）、XRD研究了超高压凝固下Mg-6Zn-1Y合金晶体形貌和凝固组织。结果表明：GPa超高压下凝固,随着凝固压力的增大,α-Mg晶体形态由1.03×0-9 GPa(常压)下的树枝晶→细树枝晶→柱状树枝晶→粒状“胞晶”的转变,固/液界面趋于稳定。1.03×10-9 GPa下实验合金的凝固组织由α-Mg相、I-Mg3Zn6Y和S-Mg43Zn4Y3相3相组成,2~6 GPa下实验合金的凝固组织由α-Mg、I-Mg3Zn6Y和S-Mg43Zn4Y3相和高Y含量的Mg-Zn-Y三元相4相组成     

时效Mg-8.14Zn-1.44Y-0.5Zr合金高温摩擦磨损性能研究

镁合金在航空航天、汽车及通讯领域有着广泛的应用, 为进一步改善镁合金的耐磨性,在不同温度下对Mg-8.14Zn-1.44Y-0.5Zr合金进行了时效处理,并测试了铸态和时效态合金的硬度及高温条件下摩擦磨损行为.采用扫描电子显微镜对不同载荷及环境温度条件下合金的摩擦磨损表面进行观察,并分析了其磨损机制.结果表明：在240 ℃时,随着时效时间的增加,合金的硬度值呈现先增加而后降低的趋势,当时效温度为240 ℃,时间为12 h时,Mg-8.14Zn-1.44Y-0.5Zr合金具有最高的硬度值; 铸态合金的磨损体积损失明显高于时效态合金,两种合金的磨损体积损失均随载荷和环境温度增加而增大,且时效态合金发生严重磨损时对应的转变温度滞后于铸态合金; 环境温度低于250 ℃时,合金的磨损机制主要为磨粒磨损和氧化磨损,环境温度为300 ℃时,磨损机制变为剥层磨损和黏着磨损.时效处理可显著提高Mg-8.14Zn-1.44Y-0.5Zr合金的硬度及耐磨性.     

Tribological properties of Cu-La_2O_3 composite under different electrical currents

A new type of Cu-La2O3 composite was fabricated by internal oxidation method using powder metallurgy.Sliding wear behavior of the Cu-La2O3 composite was studied on a pin-on-disc wear tester under various electrical currents and applied loads.The worn surfaces were characterized using scanning electron microscopy and energy dispersive spectroscopy to probe the wear mechanisms.The results indicated that applied load had a significant effect on the wear rate of the Cu-La2O3 composite pins.The wear rate displayed the minimum value at the load of 50 N during electrical sliding processes.The corresponding wear mechanism was identified to be adhesive wear,abrasive wear,oxidation wear and arc erosion.     

Investigation on the modification behavior of A356 alloy inoculated with a Sr-Y composite modifier

In the present paper, differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and X-ray diffraction (XRD) were used to examine the effects of a Sr-Y composite modifier on the microstructure of A356 alloy. After adding Y to A356, YAl 3 compounds formed, and the size of the α (Al) crystal nucleus increased. The degree of supercooling caused by Sr-Y composite modifier was higher than Sr modification by 2.7 °C, leading to an increased nucleation rate. This increase in supercooling temperature was favorable to the refinement of eutectic structure of the alloy and its eutectic reaction was delayed to the maximum extent. The Si phase in the as-cast Sr-Y composite-modified A356 alloy was either granular or flaky. No large flakes of eutectic Si were found, and the modification effects were completely comparable with those obtained using a lone Sr modifier. After T6 heat treatment, most of the eutectic Si showed a grain-like shape with smaller grains. No eutectic Si with long-strip shapes, significant enhancements in the particle roundness and evenness of the Si crystals, and increased globosity were observed. Both the roundness and evenness of the grained Si crystals were enhanced, and the amount of globular eutectic Si available increased, these findings showed that excellent modification effects were achieved.     

超高压下Mg-6Zn-1Y合金的凝固组织与性能北大核心CSCD

利用SEM、EDS、XRD研究了超高压凝固下Mg-6Zn—Y合金的凝固组织及性能。结果表明,常压下Mg-6Zn·1Y合金的宏观凝固组织为粗大的树枝晶,二次枝晶间距约为40～50μm;在GPa级超高压凝固条件下,合金的凝固组织显著细化,6GPa-1300℃凝固条件下,其二次枝晶间距仅为3～6μm;超高压下凝固的合金基体上分布的粒状相更加细小和均匀弥散,单位面积上粒状相的数量显著增多。常压下合金的显微硬度为59HV,在6GPa下超高压下合金的硬度大幅提高,达到85HV。高压下合金的弹性模量由常压下的68GPa减小到6GPa下的59GPa。     

Cu-La_2O_3复合材料的摩擦磨损特性

采用内氧化法制备Cu-La2O3复合材料。以该复合材料为销试样,轴承钢为盘试样,进行载流条件下的高速摩擦磨损试验,并对销试样摩擦表面进行微观形貌分析。结果表明:在试验条件下,Cu-La2O3复合材料的磨损率随电流的增加而增大,随载荷增加先降低后增加。复合材料的干滑动摩擦磨损机制主要是磨粒磨损、粘着磨损及电弧侵蚀磨损。